This invention relates to a refrigerant cycle having tandem compressors, wherein only some of the compressors are provided with economizer ports and can be utilized within an economizer cycle.
Tandem compressor refrigerant cycles are known, and have two or more compressors compressing refrigerant and delivering it to a common discharge manifold. Similarly, these compressors are drawing refrigerant from a common suction manifold. In some arrangements, oil equalization lines connecting oil sumps of the tandem compressors for oil management and suction pressure equalization lines connecting shells of the tandem compressors are employed. Tandem compressors provide flexibility to a refrigerant cycle designer, such as allowing additional levels of capacity control by turning off some of the compressors. Moreover, in some applications that would require a very large single compressor, tandem compressors provide design options, availability, and potential cost savings.
In refrigerant cycles having a single compressor, it is known to utilize an economizer circuit. The use of an economizer cycle provides system performance enhancement under certain conditions by tapping off a portion of a refrigerant flow downstream of a condenser. The tapped refrigerant is passed through a separate economizer expansion device, and then passes through an economizer heat exchanger along with the main refrigerant flow. The tapped refrigerant cools the main refrigerant flow, such that the main refrigerant flow has a greater cooling capacity when it reaches the evaporator. The tapped refrigerant is returned to the compressor at an intermediate point in the compression cycle. Furthermore, economizer cycles provide extra steps of unloading, closely matching capacity requirements as well as improve system reliability, enhance operation control and reduce life-cycle cost of equipment due to decreased number of system shutdowns. Furthermore, when an economizer cycle is combined with various means of compressor unloading, even greater benefits can be achieved. Although economizer circuits provide additional benefits to a refrigerant cycle as described above, the economizer circuits have not been incorporated into refrigerant cycles having tandem compressors, where some compressors are designed to have an intermediate injection port and some compressors are conventional non-economized compressors.